I am not sure who wrote this… the author just repeating what was written in Visuddhimagga.
Then it seems out of sudden the writer just pop out with a sentence claiming all Rupas are mental.
The sutta reference provided did not say anything like Rupa is mental. MN 28 Mahahatthipadopama Sutta: The Greater Discourse on the Simile of the Elephant's Footprint - Suttas.com
Arahant Sariputta Thera explaining the four great elements in details, followed by space … These five things are under Rupa. And Arahant Sariputta Thera made clear distinction between the mind and the elements. Eg:
Quote “And his mind, having made an element its objective support, enters into [that new objective support] and acquires confidence, steadiness, and decision.”
I don’t see how that sutta can be a valid support of the author’s argument on Rupa is mere mental.
Furthermore, the article wrote:
The Buddha defined rūpa as ALL those that can provide a sensory experience (viññāṇa.)
Well, I don’t think that’s how Buddha said in the scripture.
In Khajjanīyasutta (SN22.79), the Buddha actually said this:
"Kiñca, bhikkhave, rūpaṁ vadetha?
Ruppatīti kho, bhikkhave, tasmā ‘Rūpan’ti vuccati."
Then in Visuddhimagga, Bhaddantacariya Buddhaghosa Thera wrote:
Tattha yaṃ kiñci sītādīhi ruppanalakkhaṇaṃ dhammajātaṃ, sabbaṃ taṃ ekato katvā rūpakkhandho ti veditabbaṃ.
That just proved the statement made by the author not valid.
Furthermore, if Rupa is really mere mental, then we have a problem with Arupabrahma. That would mean Arupabrahma is a brahma with no mental quality.
I think the author need to study harder.